This invention relates generally to air conditioning systems. More particularly, the invention relates to an orifice structure for the fan that moves air through the enclosure that houses the outside heat exchanger of what is known as a "split" air conditioning or heat pump system and to a cover for the enclosure that incorporates the orifice structure.
In a split air conditioning system, one of the air-to-refrigerant heat exchangers of the system is located outside the space (usually outside the building) to be conditioned. The outside heat exchanger is usually contained in an enclosure that also contains the compressor and other system components. A fan in the enclosure forces a flow of air through the heat exchanger to promote heat transfer between the air and the refrigerant.
The outside heat exchanger of the typical split system is of the plate fin and tube type with the tubing arranged in some fashion around the periphery of the enclosure. The walls of the enclosure are louvered and the fan is mounted at the top of the enclosure so that the flow of air is into the enclosure through the louvered walls, through the heat exchanger and fan and out of the enclosure through an opening in the top. The fan is usually surrounded by a fan orifice. The function of the orifice is to guide the flow of air through the fan in a manner that will improve air flow efficiency and reduce radiated noise.
For a given system design and capacity, there is a certain minimum air flow required through the outside heat exchanger. The design of the outside enclosure must enable the attainment of that airflow. At the same time, other seemingly mutually exclusive considerations entering into the design of the enclosure include optimizing the air flow efficiency in order to minimize energy consumption and radiated noise, making the enclosure able to withstand adverse weather and other conditions, minimizing overall size and manufacturing cost and providing an aesthetically pleasing external appearance.
In order to minimize overall height of the enclosure, many prior art outside enclosure designs feature a fan and fan orifice recessed into the center of the heat exchanger tubing array. This is effective in reducing enclosure height but is less than desirable from an air flow perspective. Such a design can result in reduced air flow over the uppermost regions of the heat exchanger with a corresponding reduction in heat transfer effectiveness in those regions, inefficient air flow eddies and separations upstream and downstream of the fan and its orifice, energy losses and increased radiated noise.
Advances in materials technology and fabrication techniques have led to the use of plastics in a wide variety of new applications. Modern plastics can be strong, durable, damage resistant, lightweight and competitive in manufacturing cost with other materials. Moreover, the ability to easily mold plastic material has enabled the production of components in complex shapes that have previously been difficult and uneconomical to manufacture.